Hi there honeydew74,
Thanks for joining us in Apple Support Communities! We understand you're having difficulty connecting an external display to your MacBook Air. We're glad you're here, and we'd like to learn more to see how we can help.
To start, are you using an adapter to connect your display to your MacBook Air? You'll want to be sure you're using the correct cable or adapter. Have a look at this link to learn more:
Use an external display with your MacBook Air
Next, let's be sure you followed the steps in the related article linked in blue at the top left corner of this page to set up your monitor with your MacBook Air.
If you're using the right adapter and you set up your monitor correctly, but it's still not being recognized by your MacBook Air, try working through the suggestions in this support article:
If your external display isn't detected or appears blurry on your Mac
We hope this information is helpful. Don’t hesitate to follow up with us here if you have any more questions.
Cheers.